Enhancing the Analytical Selectivity of Voltammetric Technique by the Combination of Harmonic Analysis and “Fingerprint” Phase Angle Lock-in Detection

Abstract

Traditionally, the selectivity of voltammetric analysis depends on the difference of redox potential. Unfortunately, the limit of discrimination imposed by the voltammogram itself is dozens of millivolts. This suggests that it is impossible to achieve selective detection of one chemical under the interference of chemicals which have very close redox potential with the target chemical. Herein, we provided an attractive solution to this problem, using phase angle instead of potential as the basis of selectivity. Specifically, the electrochemical system was perturbed with a large-amplitude sinusoidal potential signal and the responsive current signal was subsequently analyzed in the frequency domain. This technique was termed as sinusoidal voltammetry (SV). The selective detection can be realized by quantifying the amplitude of a certain harmonic element at the characteristic "fingerprint" phase angle of each redox couple; and their phase angle difference can be regulated to be close to 90° to eliminate interferences and optimize the selective detection. Feasibility of the proposed approach was verified with a model system consisting of two ferrocene derivatives. The underlying theoretical basis was interpreted as that there are inherently several phase angle dramatic transition regions near the redox potential, and thus a minimum redox potential difference can generate a significant phase angle difference in those regions.